1. Field of the Invention
The present invention relates to a brushless DC motor with a reduced thickness.
2. Description of Related Art
FIG. 9 of the drawings illustrates a conventional brushless DC motor with an axial winding. The brushless DC motor includes an upper pole plate 10a, a lower pole plate 10a, a coil assembly 20, a rotor 30, a circuit board 40, a metal axle tube 50, and a base 60. The upper and lower pole plates 10a are mounted to two sides of a bobbin 21 of the coil assembly 20 to form a stator. The stator and the circuit board 40 are mounted around the metal axle tube 50 and thus stacked on the base 60. The rotor 30 includes a shaft 31 extended through the metal axle tube 50. A change in the polarities of a plurality of magnetic pole faces 101 on the pole plates 10a drives the rotor 30 to turn. Although such a brushless DC motor is widely used in various kinds of electronic devices, there are too many parts for the stator (including the coil assembly 20, the bobbin 21, the circuit board 40, the metal axle tube 50, and the upper and lower pole plates 10a). The parts of the stator are stacked on the base 60 and thus increase an overall thickness and overall volume of the brushless DC motor. As a result, it is difficult to further reduce the overall thickness and volume of the brushless DC motor.
The object of the present invention is to provide a brushless DC motor including a magnetic pole base and a pole plate that are respectively formed by means of punching a magnetically conductive plate. Each of the magnetic pole base and the pole plate includes a plurality of pole faces and a magnetically conductive tube. The magnetic pole base can be used as a base on which the parts of the stator are mounted, thereby reducing the number of parts of the brushless DC motor, simplifying the structure of the brushless DC motor, and reducing the manufacture cost of the brushless DC motor.
Another object of the present invention is to provide a brushless DC motor in which the magnetic pole base can be used as a base for mounting a coil assembly and a circuit board of a stator, thereby reducing the thickness of the stator in the axial direction. The overall thickness of the motor is reduced accordingly.
A further object of the present invention is to provide a brushless DC motor, wherein no positioning means of fixing means is required for the pole plate and the magnetic pole base. The pole plate and the magnetic pole base can be assembled together by two magnetically conductive tubes respectively formed on the pole plate and the magnetic pole base. The convenience and stability of assembly are increased.
To achieve the aforementioned objects, the present invention provides a brushless DC motor including a pole plate formed by means of punching a magnetically conductive plate, a magnetic pole base formed by means of punching another magnetically conductive plate, a coil assembly mounted on the magnetic pole base, a circuit board mounted on the magnetic pole base, and a rotor.
The pole plate includes a plurality of pole faces and a magnetically conductive tube. The pole faces of the pole plate are annularly located around the magnetically conductive tube of the pole plate. The magnetic pole base includes a plurality of pole faces and a magnetically conductive tube. The pole faces of the magnetic pole base are annularly located around the magnetically conductive tube of the magnetic pole base.
The magnetically conductive tube of the magnetic pole plate and the magnetically conductive tube of the pole base are securely mounted one around the other to form an axle tube. At least one bearing is received in the axle tube for rotatably holding the shaft of the rotor. The pole faces of the magnetic pole base and the pole faces of the pole plate are alternately disposed and located around the axle tube.
Other objects, advantages and novel features of this invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.